Attachment for converting semiautomatic firearms to full automatic



Oct. 30, 1951 s j KETTERER 2,572,872

ATTACHMENT FOR CONVERTING SEMIAUTOMATIC FIREARMS TO FULL AUTOMATIC Filed OCT" 8, 1948 IIHII 26 gwucm fo o Patented Oct. 30-, 1951 OFFICE ATTACHDIENT FOR CONVERTING SEMI- AUTOMATIC FIREARMS TO FULL AUTOMATIC Stanley J. Ketterer, St. Louis, Mo. Application October 8, 1948, Serial No. 53,578

1 Claim.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 1 The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

. This invention relates to an attachment for a rifle of the semi-automatic type whereby such firearm can be converted to fire fully automatic.

Some firearms are designed to fire semi-automatically, particularly military firearms, as with such firearms it is highly desirable that the load ing operation be accomplished mechanically thereby greatly increasing the rapidity of fire with a minimum of effort on the part of the shooter. In some instances however, particularly in time of war, a much higher volume of fire I may be required and if a rifle is equipped to fire only semi-automatically, such volume of fire can not be delivered.

While many attempts have been made to convert a semi-automatic firearm to fire fully automatic, such conversions as have been evolved are highly complicated mechanisms requiring fabrication to a precision of a very high order. Fur-' ther these complicated mechanisms generally re- A particular object of this invention is to profrom engagement with the hammer when the operating rod of the firearm strikes the cam associated with the lever.

The invention to be presently described in detail is preferably applied to a rifle of the type known as the U. S. rifle, cal. .30 M1 and such application is chosen to best illustrate the manner of use of this invention. Such a specific illustration should not be construed as limiting the invention solely to use with such firearm as this 2 invention may be applied to substantially all firearms equipped for semi-automatic fire; however the preferred embodiment is shown in the accompanying drawings in which:

Fig. 1 is a fragmentary longitudinal view partly in section of a firearm showing the attachment mounted thereon.

Fig. 2 is a plan view showing the method used to mount the attachment to the stock.

Fig. 3 is an enlarged view showing the locking device elements.

Fig. 4 is an enlarged front view showing the positions of the cam for automatic and semiautomatic firing.

In Fig. 1 there is shown a rifle having a semiautomatic trigger mechanism such as is embodied in the U. S. rifle, cal. .30 M1. Suchrifle comprises mainly a receiver I I], a bolt II slidably mounted for reciprocating movement in receiver I0, an operating rod I2 connected to bolt II and slidably mounted on receiver II]. A stock I3 and a trigger guard I4 complete the main elements of the firearm. Trigger guard It includes a pivoted hammer I5 secured to such trigger guard by a pin I6. A trigger I 'I is pivotally mounted on trigger guard I I and a primary sear I8 is pivotally mounted on trigger I'I, Primary sear I8 is engageable with rearwardly projecting sear engaging lugs I9 provided on hammer I5. Hammer engaging lugs 20 are provided on the upper end of trigger ll which are engageable with forwardly projecting lugs 2| on hammer I5. A spring biased plunger 22 contained within a housing 23 and mounted on trigger guard I4 is provided to bias hammer I5 forwardly from a cocked position to a fired position. The above elements are all elements of the well known U. S. rifle, cal. .30 M1 and have been briefly described to better show the cooperation of such elements with the members of this invention. I

The device of this invention comprises a leverlike member 24 pivotall mounted to stock I3 by a transverse pin 25. Such pin is located substantially in line with sear I8. Lever 24 is offset as shown at 26 in order to clear trigger guard I4 as shown in Fig. 2. Stock I3 is cut away slightly as shown in such figure to accept lever 24. An integral depending arm 21 on lever 24 just contacts primary sear I8 as shown in Fig. 1 when hammer I5 is held in the cooked position by sear I8.

A spring 28 preferably integrally formed on the underside of lever 24 near the forward end thereof projects downwardly and contacts the bottom of a recess 29 provided on the inside of stock I3. Such spring is provided to bias lever 24 upwardly for a purpose as will later appear. A normally vertically disposed cam member 30 is hinged to the forward end of lever 2% by a pin 3|. .Cam 3% projects upwardly into the path of operating rod 12 so that such cam may be contacted by a handle 32 provided on operating rod l2 as will be later described. A locking device comprising a wedge-shaped detent 33, is provided to yieldingly secure cam 30 in either an upright or depressed position. Detent 33 is engageable with a lug 34 provided on the forward end of lever 24 in a suitably shaped "notch 35 therein. A counterbored hole 36 indetent 33 is provided to receive hinge pin 3| and a spring 31 surrounding such pin. Pin 31 is provided with a head 3:; against which one end of spring 31 abuts while the other end of such spring strikes bottom of counterbored hole 26. when cam 30 is assembled to lever 24, pin 3| is pref "erab ly secured to "lug -38 by a screw 39. Thus the bias-of spring 31 against detent 33 urges=such detent inton'otch -35 oflug 34 thereby maintaining cam 30 in either'of'the two positions selected.

:"Ihose familiar with the U. S. rifle, cal. .30 M1 f8 engages hammer lugs JI'Bto hold such hammer in the cocked position. Primary sear i8 is pro- .vi deditoiretain hammer 15 in the cooked position while the trigger is still in a .ipulled rearward position. If such sear was not provided hammer "l'iwould then 'follow bolt -ll forwardly to the battery position as there would be nothing restraining such movement of hammer 15. The reason therefore is due'to the fact that the trigger cannot'be released rapidly enough after discharge of a cartridge whereby the trigger could return to a hammer engaging position before the bol"thad reached' the battery position. V

V In view of the above, full automatic fire is Dbtainedby releasing primary sear IBirom engagement with hammer l5 shortly after bolt H has reached its locked battery position without taking the finger ofi ojftrigger l1. Bolt ll howeyer..must be .in a locked battery position otherwise an unsafe condition wouldresult.

[Accordingly by raising cam 30 to the position shown in Fig. l, handle'32 of operating rod 12 .thenstrike theislope'd top surfacecof such cam .justafter .bolt II has reached the locked battery position, whereupon lever 24 .is pivoted downwardly .orin a clockwise direction as shown i'nFig. 1 .thereby moving arm-2'! in a corresponding clockwise direction. Arm 2! being in en- ,gagement with primar sear I8 rotates such sear in a counter-clockwise hammer releasing position whereupon hammer l5 goes forwardly to discharge a cartridge in the chamber of a firehausted.

arm. 0n the recoil stroke of bolt H and operating rod 12, lever 24 is raised to its normal operating position by the bias of spring 2-8 thereby again positioning cam 30 to be engaged by handle 32. of operating 10d 12 on the counter- .recoil movement of operating ;rod "[2 whereupon the release of hammer 15 is effected as just described. Such cycle of operation will continue as long .astrigger I1 is pulled rearwardly or until the cartridges contained in the clip are ex- The firearm is readily returned to its normal firing condition by simply folding down cam 30 as shown in Fig. 4 thereby permitting hammer engaginglugs 21) of trigger I! to function in a normal semi-automatic manner.

It is thus apparent to those skilled in the art thatzthere is; here provided a simple attachment readily adapted to any firearm of the semi-auto.-

matic type for converting such firearm fromsemi automaticffireto run automatic -fire or bick tosemi-autoirrraticfire as maybe desired. attachment is cheaply and easilyffabricated and is positive in operation. It is also -lde's'ired to emphasiae that such attachment can be assembled to a f rearmvnth -a-minimum of modification o'iithe existing firearm. i

JIcla'im': r I In an automatic firearm having a bolt operating element 'reciproc'aible between a battery position and a recoil position, in "combination, a spring pressed hammer *pivotally mounted in the, firearm for movement between "a cocked *pofsition and affired jpos'itionya "trigger pivotally mounted in the firearm, said trigger savings lug toyielding'ly hold "said' hammer in the-codified position when said triggeris'inan unpu'lled-pos'ition, aisearpivotally mounted toisa'iid trigger and engageable with. saidjhammer the pulled position. of .said, .trigger, a lever member pivotally mounted on .the firearm, said lever gmember'f'having .a depending arm for contacting said sear.

cam means on saidj'lever membernormally profleeting upwardly, into the ,path o fthebolt operat ing-selement iorl contact thereby during movement into battery position wherebysaid lever member isapivo tedvs-o=that1said depending arm thereon movessaid; sear to release. said hammer "from'the cocked position thereof, .spring. means operating on said :lever memberto return said cam.mean's into the pathqoftravel of I said -.bolt .oper'atingelement .upon rrecoil movement thereof, and means for pivotally mounting said means onsa'id lever :member for selective movement 7 into and out of the ipath of travel :of the bolt operating element.

STANLEY J ..REFERENCES CITED 'The following references are of record'in the file er this 1 patent: v

' UNITED'STATES PATENTS Number Name Date 2;356,-727 Reising Aug. 22,1944 2 452 .617 Wechsler Nov. 2, 1948 2,461,670 2 Williams -i Feb. 15,1949 2,465,481 Sampson et a1. e Mar. 129, .1949 

